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Procedia Engineering
Procedia Engineering 00 (2011) 000–000 Procedia Engineering 15 (2011) 5590 – 5594 www.elsevier.com/locate/procedia
Advanced in Control Engineering and Information Science
A Study of IPv6 Labeling Forwarding Model Supporting DiffServ Chin-Ling Chen a Department of Information Management, National Pingtung Institute of Commerce, Pingtung 900, Taiwan
Abstract A new Label Forwarding model is devised to enhance the fast switching for IPv6 packets requiring service differentiation. The proposed model is intended to provide more effective functions than Multi-Protocol Label switching (MPLS). The proposed model includes two parts: labeling module and capacity management module. In labeling module, the packets with the same DiffServ Code Point (DSCP) value and next-hop address can be combined into an aggregate. The performance of aggregates transmitting can be improved at each switch router by only performing cut-through peering at the label in IPv6 packet. In capacity management module, two techniques⎯ statistical multiplexing and resizing, are applied for switch router to achieve maximum link utilization.
© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of [CEIS 2011] Open access under CC BY-NC-ND license.
Keywords: Label Forwarding, DiffServ, IPv6 and statistical multiplexing
1. Introduction With the exponential growth of real-time applications such as VoIP (Voice over IP) and VoD (Video on Demand), the existing IP network cannot provide adequate quality of services (QoS) level that enduser requires. DiffServ [1] is proposed to deal with the increasing volume of traffic, providing service differentiation by classifying and aggregating the individual traffic flow at the edge of DiffServ network. Much less attention has been paid to resource management issues related to DiffServ. Supporting a
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1877-7058 © 2011 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. doi:10.1016/j.proeng.2011.08.1037
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variety of mission-critical functions requires a DiffServ to provide performance assurances, backed by service level agreement (SLA) [2-3]. SLA specifies the forwarding service that an aggregate flow should receive. MPLS (Multi-Protocol Label switching) [4] provides fast packet forwarding by integrating label switching and routing technology. MPLS use LDP (label distribution protocol) as a signaling protocol to establish one or more LSPs (label switching paths) for traffic flows. LDP assigns labels to routers that have been chosen by routing protocol. MPLS DiffServ-TE [5-9] has been proposed to accommodate multiple IP flows along the LSP via SLA. Traditional IP packet forwarding at layer 3 must parse a relatively large header, and perform a longest-prefix match to determine a forwarding path. Furthermore, it becomes increasingly difficult for traditional IP network to specify QoS requirements on a point-to-point basis. Much attention has been paid on label switching protocols that use routing, address, and address hierarchy information for cutthroughs to bypass IP forwarding [10-12]. In this paper, we develop a new Label Forwarding model to effectively transport the aggregate of IP packets with the same QoS requirement over the LSP. The labeling protocol is divided into two categories: labeling module and capacity management module. Currently, IPv6 [13] is considered as the future version of Internet Protocol. In labeling module, a triggered packet based on IPv6 is issued from sender to setup one LSP across DiffServ network. An aggregate is defined as the set of IP packets whose next hop address and DiffServ Code Point (DSCP) are the same. Once an aggregate is identified, LSR can speed up the forwarding process with the simple cut-through at label field of IP packet header. In capacity management module, labeling function labels the incoming packets based on Forwarding Base and forwards them directly onto the corresponding LSP. To efficiently manage resource in DiffServ network, we consider two mechanisms. 1) Statistical multiplexing. As a single QoS assurance applies to an aggregate, switch router can consider multiplexing all the traffic of each given aggregate together. 2) Resizing. In order to provide tight QoS assurance, router may use network resource reservation mechanisms that allocate capacity for a given aggregate. Resizing takes place in two steps: the first step measures packet loss rate and compares it with QoS objective of the aggregate. The second step examines whether the requested bandwidth of new arrival packets is greater than the available bandwidth by applying inter-aggregate multiplex technique. The advantages of label forwarding are both simple and effective. By using cut-through technology, label forwarding accelerates packet forwarding for routers just identifying 20 bits length size label, which is distributed by LDP. Routers that utilize cut-through forwarding start sending the packet immediately after reading the label information into buffer. The main benefit of forwarding the packet at once is a reduction in latency because the forwarding decision is made almost immediately after the packet is received. The rest of this paper is organized as follows. Section 2 describes the essential mechanism of label forwarding, which including both labeling module and capacity management module. Section 3 concludes this paper. 2. Label forwarding A modified IP packet header field, called the DS field, is used to replace IPv6 Traffic Class octet [13] when applied in DiffServ network. The DS field is used to designate the packet's behavior aggregate and is subsequently used to determine which forwarding treatment the packet receives. Six bits of the DS field are used as a code-point (DSCP) to select the PHB a packet experiences at each node. Since DiffServ provides QoS control for traffic based on per-class rather than per-flow, Flow Label field, therefore, is renamed to be Label Forwarding field to avoid this confusion. Label forwarding provides simple and fast
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packet forwarding capability. When a router performs label forwarding it directly looks up forwarding base with the use of 24-bit length label forwarding field in IPv6 packet header [13]. Label forwarding can be divided into two parts: labeling module and capacity management module, which will be described in detail at section 2.1 and 2.2, respectively. 2.1. Labeling module The labeling module uses signaling protocol to dynamically distribute labels among routers across DiffServ domain. Each router maintains three types of routing and label information: routing table (RT), label base (LB) and. forwarding base (FB). Forwarding base records the label information on the specified output link. Three types of messages are transferred within IPv6 triggered packets between nodes. They are Request for label (Router options), Label transfer (Destination option), and ACK (Hopby-Hop option) message. The labeling protocol is designed in the way that the upstream node asks the downstream node to allocate a label for a specific aggregate. The label needs to be transferred in its own IPv6 packet from the downstream node to the upstream node. Label protocol obtains the output port information from routing table and provides forwarding base the label information with the identity of output port on which packets is to be forwarded. The trigger IP packet starts the setup of LSP operation. The trigger packet has a Router option header, which contains Request for label message in its header chain. Core router receives this message and allocates a 24-bit label to be used for this specific aggregate, which is based on the label base and routing table. Core router sends a Label transfer message to Ingress router. The label is passed to Ingress router in the IPv6 Destination Options header. After then, core router continues the operation of label switching downstream across DiffServ domain. Finally, the trigger packet reaches Egress router. Egress router responds ACK message (Hop-by-Hop option header), which is based on Routing option header, back to Ingress router. Upon Ingress router receiving this packet, it knows the dedicated LSP is set up and then starts to transmit packets belonging to LSP. The label that is carried within every IPv6 packet is needed to switch in each router within DiffServ network. 2.2. Capacity management module Capacity management module consists of four components: Classifier, Labeling function, Meter and MUX. The data packet arrives at input port adapter. The classifier function, which peeks the incoming packet header, identifies packets that are to be afforded special service based on DSCP and classifies them belonging to the specific aggregate. The aggregated packets are defined by the destination address and DSCP. Upon receiving the aggregate packets, label function first extracts the label information from label field. The value carried in the field identifies outgoing link to which data packets will eventually be sent. Each aggregate is assigned a unique entry in the forward base, with pointers to the label destined to output port. Edge LSR receives packet, performs label switching. Ingress DER first finds out the entry for destination and LSP next-hop. Edge LSR applies label and decides output interface. Destination IP is found in routing table/forwarding base on Ingress router. In the proposed model, link is defined as the physical connection between two routers within DiffServ network. Link capacity is W bit/s. We consider that there are five classes of aggregates (i.e., EF, AF1, AF2, AF3 and AF4) supported over the link. Each aggregate supports sources with similar class of traffic. Link capacity is proportionally allocated five classes of aggregates. Table 1 indicates Parameter/Class mapping table.
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4 Table 1. Parameter/Class mapping table Parameter/Class
EF
AF1
AF2
AF3
AF4
j
0
1
2
3
4
Bandwidth differentiation ratio
σ・
σ1
σ2
σ3
σ4
Assume Wf(j) indicate the fixed bandwidth assigned for the aggregate j at initiation. We have Wf(j) = W × (σj /Σσj)
(1)
Meter measures the arrival process via its count process, which keeps account of the number of arrival packets in consecutive time periods. Assume Wa(j) is the actual bandwidth allocated on aggregate j at time t. Meter calculates the capacity Wa(j) for the aggregate j using on-line traffic measurement. The values are then used as inputs to MUX, which calculates the capacity for the combined aggregates. Assume Wt(j) indicate effective bandwidth sufficient to meet the QoS requirement, εj, for aggregates j on the link. MUX calculates Wt from the used capacity of each aggregate Wa(j) and then produces interaggregate multiplexing gain G as follows. G = (ΣWf(j) −ΣWt(j))/N,
(2)
where N is the number of aggregates to be multiplexed. Assume Wnew(j) is the capacity calculated for new arrival packets onto aggregate j during the time period Δt. MUX will make decision to accept or discard the new arrival packets onto aggregate j during the period Δt based on the following equation:
φ(j)＝Wf(j)＋G－Wa(j)－Wnew (j), If the value of φ(j) is greater than or equal zero, the new arrival packets during time period Δt will be accepted; otherwise it will be rejected. 2.3. Adapted network measurement mechanism We also propose an adapted network measurement mechanism, in which the variable-size measuring period is adjusted based on the network status. The measuring period Δt has m time-units initially and increases n time-unit whenever it detects overloaded state. The measuring period m controls the sensitivity of packet arrival rate. The smaller the measuring period is, the more sensitive the bursty traffic can be policed. The larger the measuring period is, the smoother the traffic appears. That is, the measuring period is much less than the shortest burst length and is much greater than the time of transmitting a minimum packet size. The network measurement is used to detect whether network status reaches an overload state, which indicates the packets loss QoS, εj, cannot be satisfied. In the case of overload state, window size will be reset to optimum size according to packet loss and bursty packet arrival rate. When the mechanism detects the overload state, the size of measuring period is reset to a new value, which is computed from the bursty packet interval of the multiplexed traffic. The bandwidth assigned to each class is based on the minimum capacity to support N aggregates, which is under the hypothesis is that the load generated by the N aggregates could be approximated by a variable with Gaussian distribution [14]. In the proposal, a new dynamic bandwidth and buffer allocation is proposed to assign the bandwidth Ci to each traffic class. The function is used to adjust the bandwidth assignment
(3)
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each time. In order to maximize the bandwidth utilization of link, Wt(j) must be minimal while the required QoS, εj, is guaranteed. 3. Conclusion This paper proposes a way to dynamically allocate the aggregate reservation, classify the traffic for which the aggregate reservation applies, determine how much bandwidth is needed to achieve maximum network utilization and recover the bandwidth in case the flow reservations are no longer required. By using IPv6 Routing option headers, the acknowledgement information of triggered packet can be traced back to the source without difficulty. The advantages of the proposed model are described as follows. First, efficient transportation of IP packets could be obtained by applying labeling forwarding, using Flow Label field within IPv6 header without any modification. Second, the lightweight label signaling protocol is simple by only using IPv6 triggered packet to setup LSP across DiffServ domain without the need of any signaling protocol for MPLS. Third, the proposed model can achieve significant multiplexing gains in DiffServ network, by dynamically sizing aggregate and network capacity. In the future, we will do some experiments in comparing the performance of the proposed scheme with that of MPLS in transmitting the aggregate. References [1] Grossman D. New Terminology and Clarifications for DiffServ. IETF RFC 3260, April 2002. [2] Fernandez MP, Pedroza ACP, Rezende JF. QoS provisioning across a diffserv domain using policy-based management. GLOBECOM 2001 - IEEE Global Telecommunications Conference; 1: 2220-2224. [3] Marchese M, Raviola A, Mongelli M, Gesmundo V. IP switching enhancements over IP differentiated services for QoS interworking. MILCOM 2007 - IEEE Military Communications Conference; 1: 1552-1558. [4] Smith D, Mullooly J, Jaeger W, Scholl T. Label Edge Router Forwarding of IPv4 Option Packets. IETF RFC 6178, March 2011. [5] Faucheur FL, Lai W. Maximum Allocation Bandwidth Constraints Model for Diffserv-aware MPLS Traffic Engineering. IETF RFC 4125, June 2005. [6] Goyal S, Bellur U. Mapping application QoS to network configurations for MPLS networks. CCNC 2005 - IEEE Consumer Communications and Networking Conference; 1: 562-564. [7] Alshaer H, Horlait E. Dimensioning network resources in DiffServ over MPLS based expedited forwarding service subclasses. IM 2005 - IFIP/IEEE International Symposium on Integrated Network Management; 1: 1161-1164. [8] Ashour M, Tho LN. Delay-margin based traffic engineering for MPLS-DiffServ networks. Journal of Communications and Networks; 10, 3: 351-361. [9] Kashihara S, Miyazawa M, Ogaki K, Otani T. Proposal of the architecture of a QoS assured network by cooperating between IP flow control and MPLS DiffServ-TE. ICC 2009 - IEEE International Conference on Communications; 32, 1; 1138-1143. [10] Boustead P, Chicharo J. Label switching using the IPv6 address hierarchy, GLOBECOM 2000 - IEEE Global Telecommunications Conference; 1: 500-504. [11] Marchese M, Raviola A, Mongelli M, Gesmundo V. IP switching enhancements over IP differentiated services for QoS interworking, MILCOM 2007 - IEEE Military Communications Conference; 1: 1552-1558.. [12] Chakravorty S. Challenges of IPv6 flow label implementation. MILCOM 2008- IEEE Military Communications Conference; 27, 1: 2496-2501. [13] Hu Q, Carpenter B. Survey of Proposed Use Cases for the IPv6 Flow Label. IETF RFC 6294, June 2011. [14] Lee S, Song J. A measurement-based admission control algorithm using variable-sized window in ATM networks. Computer Communications; 1998, 21, 2: 171-178.
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